%0 Journal Article
%T A Combined Softening and Hardening Mechanism for Low Frequency Human Motion Energy Harvesting Application
%A Khalis Suhaimi
%A Roszaidi Ramlan
%A Azma Putra
%J Advances in Acoustics and Vibration
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/217032
%X This paper concerns the mechanism for harvesting energy from human body motion. The vibration signal from human body motion during walking and jogging was first measured using 3-axes vibration recorder placed at various places on the human body. The measured signal was then processed using Fourier series to investigate its frequency content. A mechanism was proposed to harvest the energy from the low frequency-low amplitude human motion. This mechanism consists of the combined nonlinear hardening and softening mechanism which was aimed at widening the bandwidth as well as amplifying the low human motion frequency. This was realized by using a translation-to-rotary mechanism which converts the translation motion of the human motion into the rotational motion. The nonlinearity in the system was realized by introducing a winding spring stiffness and the magnetic stiffness. Quasi-static and dynamic measurement were conducted to investigate the performance of the mechanism. The results show that, with the right degree of nonlinearity, the two modes can be combined together to produce a wide flat response. For the frequency amplification, the mechanism manages to increase the frequency by around 8 times in terms of rotational speed. 1. Introduction The significant reduction in power consumption to operate mobile gadgets and wireless sensors has induced vast research interest in harvesting energy from ambient sources. Scavenging energy from ambient vibration is one of the examples. Most vibration based scavenging device is traditionally configured as a linear resonant generator that consists of a single degree of freedom (SDOF) mass-spring-damper system. This particular generator is particularly useful for high frequency applications as well as when the ambient frequency does not vary with time. The optimum power of the linear resonant generator can only be obtained when the natural frequency of the device matches the excitation frequency. A Slight mismatch between these two frequencies may lead to a large reduction in the power harvested [1]. Researchers have introduced tuning techniques into the generator so that the natural frequency of the device can be changed according to the input frequency. Eichhorn et al. [2] used a prestress mechanism that can passively be adjusted by rotating a screw to alter the device natural frequency. An active tuning method proposed by Zhu et al. [3] utilized a microcontroller that can adjust the separation of interacting magnets to alter its natural frequency. However, active tuning may induce complex tuning scheme and
%U http://www.hindawi.com/journals/aav/2014/217032/